This paper considers a MIMO secure wireless communication system aided by the
physical layer security technique of sending artificial noise (AN). To further
enhance the system security performance, the advanced intelligent reflecting
surface (IRS) is invoked in the AN-aided communication system, where the base
station (BS), legitimate information receiver (IR) and eavesdropper (Eve) are
equipped with multiple antennas. With the aim for maximizing the secrecy rate
(SR), the transmit precoding (TPC) matrix at the BS, covariance matrix of AN
and phase shifts at the IRS are jointly optimized subject to constrains of
transmit power limit and unit modulus of IRS phase shifts. Then, the secrecy
rate maximization (SRM) problem is formulated, which is a non-convex problem
with multiple coupled variables. To tackle it, we propose to utilize the block
coordinate descent (BCD) algorithm to alternately update the TPC matrix, AN
covariance matrix, and phase shifts while keeping SR non-decreasing.
Specifically, the optimal TPC matrix and AN covariance matrix are derived by
Lagrangian multiplier method, and the optimal phase shifts are obtained by
Majorization-Minimization (MM) algorithm. Since all variables can be calculated
in closed form, the proposed algorithm is very efficient. We also extend the
SRM problem to the more general multiple-IRs scenario and propose a BCD
algorithm to solve it. Finally, simulation results validate the effectiveness
of system security enhancement via an IRS.

本文研究了一种采用物理层安全技术发送人工噪声（AN）的 MIMO 保密无线通信系统，其中引入了高级智能反射表面（IRS），利用分块协调下降算法（BCD）来最大限度地提高系统保密性能。

智能反射面辅助的安全 MIMO 无线通信

Artificial-Noise-Aided Secure MIMO Wireless Communications via  Intelligent Reflecting Surface

Due to the malicious attacks in wireless networks, physical layer security
has attracted increasing concerns from both academia and industry. The research
on physical layer security mainly focuses either on the secrecy
capacity/achievable secrecy rate/capacity-equivocation region from the
perspective of information theory, or on the security designs from the
viewpoints of optimization and signal processing. Because of its importance in
security designs, the latter research direction is surveyed in a comprehensive
way in this paper. The survey begins with typical wiretap channel models to
cover common scenarios and systems. The topics on physical-layer security
designs are then summarized from resource allocation, beamforming/precoding,
and antenna/node selection and cooperation. Based on the aforementioned
schemes, the performance metrics and fundamental optimization problems are
discussed, which are generally adopted in security designs. Thereafter, the
state of the art of optimization approaches on each research topic of physical
layer security is reviewed from four categories of optimization problems, such
as secrecy rate maximization, secrecy outrage probability minimization, power
consumption minimization, and secure energy efficiency maximization.
Furthermore, the impacts of channel state information on optimization and
design are discussed. Finally, the survey concludes with the observations on
potential future directions and open challenges.

对物理层安全设计的一次全面调查研究，包括 typical wiretap channel 模型的典型场景和系统，从资源分配，波束成形 / 预编码，和天线 / 节点选择和协作三个方面总结了物理层安全设计的主题，并从密度速率最大化、安全超时概率最小化、功耗最小化和安全能效最大化四个优化问题分类的最新优化方法进行了回顾，并讨论了信道状态信息对优化和设计的影响，最后总结了未来研究方向和挑战。